This invention relates, generally, to airfoils and, more particularly, to tandem airfoils.
Airfoils may be employed in, for example, power turbines, compressors or aircraft engines. Vanes and blades are examples of airfoils. A blade, which may also be referred to as a "bucket" or "rotor," may comprise an airfoil mounted to a wheel or disk, for rotation about a shaft. In addition, a vane, which may be referred to as a "nozzle" or "stator," may comprise an airfoil mounted in a casing surrounding or covering the shaft about which the blade rotates. Typically, a series of blades may be mounted about the wheel at a particular location along the shaft. Furthermore, a series of vanes may usually be mounted upstream (e.g., relative to a general flow direction) of the series of blades, such as for maximizing efficiency of fluid (e.g., gas) flow. Such an arrangement of vanes succeeded by blades may be referred to as a "stage."
For example, a number of stages of vanes and blades may be located in a compressor in order to compress gas (e.g., air), to be mixed and ignited with fuel, such as to be delivered to an inlet of a turbine. The turbine may include a number of stages of vanes and blades in order to extract work from the ignited gas and fuel. The fuel may comprise, for example, natural gas or oil. Further, the addition of the fuel to the compressed gas may comprise a contribution of energy to the combustive reaction, that may raise the temperature of the gas to, for example, 3000 to 3500 degrees Fahrenheit, the product of this combustive reaction then flows through the turbine.
In order to withstand high temperatures, produced by combustion an airfoil in the turbine may include a hollow therein or passage therethrough for receiving coolant. Exemplary cooling designs include air-cooling, steam-cooling, open-circuit cooling, closed-cooling or film-cooling configurations.
Previous manufacturing techniques for relatively large vanes often have difficulties in achieving uniform wall thickness. Non-uniform wall thickness often creates inefficiencies in gas compression and a corresponding loss of extracted work.
Accordingly, a need in the art exists for airfoils allowing formation over a large range of sizes. A further need exists for such vanes whose formation provides cooling and uniform wall thickness, or better controlled wall thickness.